1. Field of the Invention
The present invention relates to a shielded magnetic head of an active system with high sensitivity and a high-density magnetic reproducing apparatus utilizing variations in high-frequency impedance.
2. Related Background Art
FIG. 6 shows the operating principle of an MI (magneto-impedance) head described in The Technical Report MR95-80 published by The Institute of Electronics, Information and Communication Engineers. The MI head employs a magnetic impedance element utilizing variations in magnetic impedance. In FIG. 6, a detecting conductor 20 formed of a conductive metallic thin film is interposed across a track width T between soft-magnetic cores 21a and 21b. The soft-magnetic cores 21a and 21b are formed of a laminated film of a permalloy film P and a SiO2 film S. A high-frequency signal is applied from a high-frequency oscillator 22 for the UHF band via a resistor 23 so that the detecting conductor 20 is fed with a current 24. Terminals 25 and 26 are disposed at opposite ends of the detecting conductor 20, respectively. Therefore, variations in magnetic impedance between the terminals 25 and 26 are detected as variations in voltage between the terminals 25 and 26.
When there is no signal magnetic field generated from magnetization 28 on a magnetic recording medium 27, only a voltage according to a UHF carrier signal is generated between the terminals 25 and 26. The voltage corresponds to the product of impedance between the terminals 25 and 26 of the detecting conductor 20 and the current 24. When a signal magnetic field from the magnetic recording medium is applied, since an easy axis direction of the soft-magnetic cores 21a and 21b is oriented in a track width direction, the magnetization is tilted from the original orientation direction by the signal magnetic field to reduce magnetic impedance. Hence, a UHF carrier signal is detected in its amplitude-modulated state by the signal magnetic field of the magnetic recording medium. By amplitude-demodulating this signal, the signal magnetization 28 on the magnetic recording medium 27 can be read.
Realization of this head holds the potential of obtaining an output about ten times that of a giant MR (magnetoresistive) head. FIG. 7 is a graph showing an operating curve of the element shown in FIG. 6. This operating curve was obtained by setting a carrier signal frequency to 1.0 GHz, placing the above-described element in a central portion of a Helmholtz coil, and applying a dc magnetic field to the element. As seen from FIG. 7, in order to reproduce signals with good sensitivity and obtain waveforms with reduced distortion, a direct-current magnetic bias 29 needs to be set. In the above-described model, a direct current field is generated by the Helmholtz coil and used as a bias.
This method, however, has been disadvantageous with respect to the following points: reduction in dimension of the detecting conductor 20, particularly, in cross-sectional area, considerably increases a value of resistance; and reduction in thickness of the soft-magnetic cores 21a and 21b around the detecting conductor 20 reduces inductance, namely, impedance. Moreover, in order to improve track recording density, it has been requested that a detecting part be positioned closely to the magnetic recording medium 27, and that a shielded magnetic head configuration can be applied where a strong signal magnetic field from a medium is detected.
Thus, a magnetic head with high sensitivity that allows high-density recording has been requested. The achievement of this requires the development of a new detecting method utilizing variations in impedance at a high frequency and the clarification of the operating characteristics of the method.
It is an object of the present invention to provide a shielded magnetic head with excellent resolution and high sensitivity that can detect, by utilizing variations in impedance at a high frequency, only an impedance component that varies depending on a signal magnetic field.
In order to solve the afore-mentioned problems, a shielded magnetic bead of the present invention includes a magnetically shielded gap and first to fourth conductive magnetic films disposed in the gap. The first to fourth conductive magnetic films, each extending parallel to a tip face of the magnetic head to be opposed to a magnetic recording medium, are aligned at a distance from one another in a direction perpendicular to the tip face so as to be away from the tip face in ascending order and connected to one another so as to form a bridge circuit. The distance between the first conductive magnetic film and the tip face is set so that a signal magnetic field from the magnetic recording medium is applied to the first conductive magnetic film.
In this magnetic head, preferably, the distance between the respective conductive magnetic films is set so that a signal magnetic field from the magnetic recording medium is applied substantially only to the first conductive magnetic film.
The above-described magnetic head preferably includes: a pair of shielding soft-magnetic materials on opposite sides of the gap; means for applying a direct current field to the first to fourth conductive magnetic films; first and second electrode terminals for feeding a high-frequency carrier signal to the bridge circuit; third and fourth electrode terminals for detecting the bridge output of the bridge circuit; a high-frequency oscillator connected to the first and second electrode terminals, which outputs the high-frequency carrier signal; and a high-frequency amplifier connected to the third and fourth electrode terminals. Variations in impedance of the first conductive magnetic film depending on a signal magnetic field from the magnetic recording medium are detected as variations in the high-frequency carrier signal.
It is preferable that effective permeability of the shielding soft-magnetic materials at a frequency of the high-frequency carrier signal be smaller than that of the conductive magnetic films. Further preferably, the conductive magnetic films have a thickness equal to or less than skin depth at a frequency of the high-frequency carrier signal.
Furthermore, it is preferable that the respective shielding soft-magnetic materials include a first magnetic material disposed on a face opposed to the conductive magnetic films and having excellent high-frequency characteristics and a second magnetic material disposed on an outer side of the first magnetic material, which responds to a signal applied from a magnetic recording medium.
Moreover, preferably, a high-frequency carrier signal current with a direct current for a direct-current magnetic bias being superimposed is applied to the conductive magnetic film. As an alternative, a permanent magnet may be provided for applying a direct-current bias magnetic field in a direction perpendicular to the tip face to the first to fourth conductive magnetic films.
A magnetic reproducing apparatus of the present invention includes: a shielded magnetic head configured according to any one of the above-described configurations; a retention member for retaining a recording medium on which signals are recorded magnetically; and a positioning member for positioning the shielded magnetic head at a predetermined position with respect to the recording medium.